The energy balance of a forested tropical island site was determined using the Bowen ratio technique. The site on the Tiwi Islands consisted of a 12 m tall, tropical eucalypt forest with some mixed conifers. This site represents the dominant vegetation type on the islands. Standard flux measurements were made over a 100 day period extending from the monsoon transition period (November) through to monsoon end (March). Results presented here are from an initial ten day period of intensive measurements.
During the intensive measurement period a large amount of total daily net radiation (11.95 MJ.m-.day-1) was available at the site which was partitioned predominately into latent heat (7.09 MJ.m-2.day-1). Daily evapotranspiration from the site averaged 2.95 mm.day-1. The variation in the daily magnitude of evapotranspiration was determined by the variation in daily net radiation, which in turn was driven by local- and regional-scale cloudiness. Sensible heat flux totalled 4.62 MJ.m-2.day-1 with the Bowen ratio remaining fairly constant over the measurement period at ~0.65. The total daily soil heat flux of 0.24 MJ.m-2.day-1 represented a slight net storage through the period. On a daytime basis soil heat flux comprised 4.4% of net radiation. Canopy-air heat storage was also measured and comprised 1.0% of the net radiation on a daytime basis. On an hourly basis this was as high as 30% of net radiation at sunrise and sunset. Canopy-air heat storage reached a maximum of 17.9 W.m-2 at 0740 local standard time and a minimum of -23.7 W.m-2 at 1430 local standard time when environmental conditions are modified by local diurnally-modulated thunderstorms.
Both aspirated and un-aspirated thermocouples were used to determine the temperature gradient above the canopy. It was found that the unaspirated thermocouples were subject to differntial cooling through increasing wind speeds away from the canopy. Aspirated thermocouples are recommended for use in similar forested environments.